The present invention generally relates to methods of detecting a position on a disk, disk units and disks, and more particularly to a method of detecting a position on a disk which is time-divisionally recorded with a data region and a servo region based on a signal read from the disk, a disk unit which employs such a method, and a disk for use in such a disk unit.
Conventionally, there was a method of detecting a position on a magnetic disk by recording 4 kinds of servo mark patterns in a servo region of the magnetic disk. According to this method, an operation is carried out with respect to reproduced signal waveforms of 2 kinds of servo mark patterns out of the 4 kinds of servo mark patterns reproduced by a head, and the detection on the magnetic disk is detected based on a result of the operation. However, since each position on the magnetic disk is detected based on the reproduced signal waveforms of 2 kinds of servo mark patterns out of the 4 kinds of servo mark patterns, there was a problem in that the utilization efficiency of the servo information is poor. In addition, when the head makes a scan so as to traverse cylinders on the magnetic disk during a seek operation or the like, there was a problem in that it is impossible to accurately detect the position on the magnetic disk.
On the other hand, a method of recording the servo mark pattern in 3 kinds of position regions EVEN1, ODD and EVEN2 in the servo region on the magnetic disk has recently been proposed. When a period of a clock is denoted by T, the servo mark pattern is recorded with a period of 8T ("10001000") as a base so that a phase shifts by 45.degree. per 1 cylinder. As a result, it is possible to detect the position on the magnetic disk based on the phase of the servo mark pattern which is reproduced by the head, and the utilization efficiency of the servo information is improved. In addition, even in a case where the head traverses the cylinders on the magnetic disk, it is possible to accurately detect the position on the magnetic disk based on the phase of the servo mark pattern which is reproduced by the head. This kind of method of detecting the position on the magnetic disk is sometimes referred to as a phase demodulation technique.
However, in the proposed method described above, a demodulating circuit with respect to the servo information and a demodulating circuit with respect to the data are provided independently. For this reason, there was a problem in that the circuit scale of the demodulating system becomes large, thereby increasing the cost of the disk unit.
Further, the demodulating circuit with respect to the servo information uses a circuit which is set and reset depending on the servo information reproduced by the head, and is designed to convert a time interval between the setting and the resetting to the position information. As a result, there was another problem in that it is impossible to accurately detect the position on the magnetic disk depending on a scanning speed of the head.